The invention relates to a catalytic method of preparing di-organo-magnesium compounds by the reaction of magnesium hydride, or of magnesium and hydrogen, with olefins.
Di-organo-magnesium compounds are usually prepared from Grignard compounds by disproportioning them with dioxane or other Lewis bases (K. Nutzel in Houben-Weyl, "Methoden der organischen Chemie", Vol. 13/2a, p. 197). EQU 2RMgX.fwdarw.R.sub.2 Mg+MgX.sub.2 ( 1)
According to U.S. Pat. No. 4,069,267 and the patent literature cited therein, di-organo-magnesium compounds can be prepared by the reaction of magnesium with alkyl halides followed by reaction with lithium alkyls in hydrocarbons. A disadvantage of this last-named method is the need to use expensive lithium alkyls.
Attempts to prepare di-organo-magnesium compounds directly from magnesium, olefin and hydrogen have hitherto achieved little success. According to H. E. Podall and W. E. Foster (J. Org. Chem., 23, 1848 (1958)), an uncatalyzed reaction of magnesium hydride with ethylene and other alpha olefins in various media and under various reaction conditions produces dialkyl magnesium compounds in poor yields. If, for example, a magnesium hydride synthesized from magnesium and hydrogen or by other methods is reacted with ethylene, only 4 to 7% of diethyl magnesium is obtained. The maximum yield of diethyl magnesium, of 28%, is achieved only when so-called "active magnesium hydride" is used, which is prepared from lithium aluminum hydride and diethyl magnesium. Accordingly, this synthesis assumes the use of diethyl magnesium prepared by some other method as the starting material.
An addition of magnesium hydride onto olefins and alkynes in tetrahydrofuran catalyzed with 5 mole-% of bis(cyclopentadienyl)titanium dichloride (Cp.sub.2 TiCl.sub.2) has been reported recently (E. C. Ashby, T. Smith, J.C.S. Chem. Comm., 30 (1978)). In this case, too, however, an "active magnesium hydride" prepared from diethylmagnesium and LiAlH.sub.4 was used. Therefore these methods are not used in the preparation of di-organo-magnesium compounds on a technical scale.
According to U.S. patent application Ser. No. 8,739 filed Feb. 2, 1979, now abandoned, the disclosure of which is incorporated herein by reference, magnesium and hydrogen can be transformed catalytically under mild conditions to magnesium hydride in tetrahydrofuran, for example, by using as catalysts combinations of a compound of a transition metal of the fourth to eighth secondary groups and an organometallic compound or a hydride of a metal of the first to third principal groups of the periodic system. If desired, the hydrogenation is performed in the presence of an activator such as, for example, a polycyclic aromatic compound and/or a tertiary amine.